Using feed thru lugs to feed a panel?

[jaggedben]

I don't think that the 2020 language actually changes anything here.

 

[PWDickerson]

Why not just do a feeder tap in the middle panel, tapping the conductors coming from the MDP? Set a fused disconnect for the solar next to the middle panel. Budda bing, budda bang!

 

[pv_n00b]

I love how every thread with a feed thru lug question ends up being more than 2 pages long.

 

[tortuga]

Thank you all for your ideas! I really appreciate it.
With all due respect:

• When a sentence opens with "Where" and you don't have the "Where" you ignore the sentence.
• Keep in mind the middle panel creates two feeders per def of feeder art 100. Call them 1and 2 see 1-line (post #28).
• 705.12(B)(3) states I only need to use "one" of the methods listed.
• 705.12(B)(3)(6) contains two sentences.
• The first sentence of 705.12(B)(3)(6) remains standing without being qualified by the second.
• The second sentence of 705.12(B)(3)(6) only servs to give more options in the specific case "Where overcurrent device is installed at the supply end of the feed-though conductors … " so not this case, then disregard.
• The feed-through conductors (Feeder #2 in post #28) then can now only be sized in accordance with the first sentence of 705.12(B)(3)(6)
• Therefore I can use 705.12(B)(1) (a) or (b)

705.12(B)(1) (b)
"an an overcurrent device at the load side of the power source connection point shall be rated not greater than the ampacity of the feeder"

4/0 AL protected by the 200A OCPD in loadcenter "B" (see 1-line in post #28) meets 705.12(B)(1) (b).
4/0 AL protected by the 200A OCPD in loadcenter "A" (see 1-line in post #28) meets 705.12(B)(1) (b).
QED

Please let me know what you think about this specific argument, as I have probably failed to see the train heading right at me.
Happy Friday
Cheers

 

[wwhitney]

The first sentence of 705.12(B)(3)(6) remains standing without being qualified by the second.
The second sentence of 705.12(B)(3)(6) only servs to give more options in the specific case "Where overcurrent device is installed at the supply end of the feed-though conductors … " so not this case, then disregard.

I agree with you that the above should be true. However, you have to allow for the fact that the NEC is illogically often written. Under your interpretation, the last sentence of 705.12(B)(3)(6) would be meaningless, as it grants permissions that you already have. And the first sentence would automatically qualify any panel with feed through lugs and conductors. Both of those conclusions are nonsensical.

So instead, 705.12(B)(3)(6) must be read as intending to mean "Connections shall be permitted on busbars of panelboards that supply lugs connected to feed-through conductors (only if you comply with the rest of the section.) The feed-through conductors shall be sized in accordance with 705.12(B)(1). Where an overcurrent device is installed at the supply end of the feed-through conductors, the busbar in the supplying panel board shall be permitted to be sized in accordance with 705.12(B)(3)(1) through 705.12(B)(3)(3) (otherwise, it is not permitted, and you can't comply with 705.12(B)(3))."

BTW, seems like 705.12(B)(3)(6) is a step backwards as far as 705.12(B)(3)(1) goes. I don't see any issue that feed through lugs cause when a panel complies with 705.12(B)(3)(1). So there should be not further restrictions or requirements for OCPD on the feed through conductors to qualify the busbar via 705.12(B)(3)(1).

Cheers, Wayne

 

[ggunn]

I agree with you that the above should be true. However, you have to allow for the fact that the NEC is illogically often written. Under your interpretation, the last sentence of 705.12(B)(3)(6) would be meaningless, as it grants permissions that you already have. And the first sentence would automatically qualify any panel with feed through lugs and conductors. Both of those conclusions are nonsensical.

So instead, 705.12(B)(3)(6) must be read as intending to mean "Connections shall be permitted on busbars of panelboards that supply lugs connected to feed-through conductors (only if you comply with the rest of the section.) The feed-through conductors shall be sized in accordance with 705.12(B)(1). Where an overcurrent device is installed at the supply end of the feed-through conductors, the busbar in the supplying panel board shall be permitted to be sized in accordance with 705.12(B)(3)(1) through 705.12(B)(3)(3) (otherwise, it is not permitted, and you can't comply with 705.12(B)(3))."

BTW, seems like 705.12(B)(3)(6) is a step backwards as far as 705.12(B)(3)(1) goes. I don't see any issue that feed through lugs cause when a panel complies with 705.12(B)(3)(1). So there should be not further restrictions or requirements for OCPD on the feed through conductors to qualify the busbar via 705.12(B)(3)(1).

Cheers, Wayne

Kirchoff's current laws are at the base of the NEC rules and should be considered when interpreting the code.

 

[tortuga]

Interesting, well I summited a plan Friday to the AHJ that has a polished up one line like post #28.
Going back to the 2nd sentence with more caffeine this morning
"Where overcurrent device is installed at the supply end of the feed-though conductors "
I am thinking since you can have two panels next to each other and use feed thru lugs to feed main lugs of the second panel.
An overcurrent device 'at the supply end ' can be a main breaker in the second panel, and that stops that buss from overloading.

Kirchoff's current laws are at the base of the NEC rules and should be considered when interpreting the code.

My attempt at that is the blue arrows in the diagram in post #28

 

[wwhitney]

Kirchoff's current laws are at the base of the NEC rules and should be considered when interpreting the code.

Agreed in principle (mostly for interpreting the ambiguous), but what conclusion you draw from that which bears on my quoted post escapes me.

Cheers, Wayne

 

[ggunn]

Agreed in principle (mostly for interpreting the ambiguous), but what conclusion you draw from that which bears on my quoted post escapes me.

Cheers, Wayne

Sorry; I should have just entered a post instead of replying to yours. Apologies.

 

[tortuga]

From the perspective of Kirchoff's current law the feed thru panel sees no different current than a end of the run panel?
Edit: as long as there is an OCPD protecting the feed-though conductors

 

[gene6]

So instead, 705.12(B)(3)(6) must be read as intending to mean

I don't think its on us as electricians to read into what the NEC intends, if 705 is so bad we have to read into what it intends, thats a legally ambitious territory.
What the OP is proposing no inspector can refute and if he appealed an AHJ he would prevail in court.

 

[jaggedben]

I don't think its on us as electricians to read into what the NEC intends, if 705 is so bad we have to read into what it intends, thats a legally ambitious territory.
What the OP is proposing no inspector can refute and if he appealed an AHJ he would prevail in court.

Not to get too philosophical, but you always have to read intention into the words in any book. That's the nature of language.

What Wayne is saying is that the way it's written, there's only one logical way to interpret it. "Where [you have x], [y] shall be permitted." has to be read as "If you don't have x, y is not necessarily permitted." This section may violate some NFPA style manual, or perhaps the style manual needs to be updated to require clear language. But Wayne is right, you can't just ignore a sentence that was obviously put in there to mean something.

 

[tortuga]

My my philosophical argument is the main breaker in the last panel is still at the supply end of the feed thru conductors.

 

[gene6]

you always have to read intention into the words in any book. That's the nature of language.

Not in a court room, show that sentence to a lawyer, It not enforceable.
I am not a PV guy here, but code is a law all the OP needs to do is comply with the law.

 

[tortuga]

My plans got approved!
Yay!
Thanks again all
Work safe out there.

 

[wwhitney]

My philosophical argument is the main breaker in the last panel is still at the supply end of the feed thru conductors.

That would depend on what "supply" means. If "supply" means grid, I don't see how you can defend that interpretation. But if the PV were interconnected in the subpanel, you could argue that "supply" actually means the alternate source (PV) in that sentence, and so the subpanel main breaker would be at the supply end of the feed-thru conductors.

Cheers, Wayne

 

[jaggedben]

Not in a court room, show that sentence to a lawyer, It not enforceable.
I am not a PV guy here, but code is a law all the OP needs to do is comply with the law.

And courts consider the intention of the law all the time.

 

[jaggedben]

My my philosophical argument is the main breaker in the last panel is still at the supply end of the feed thru conductors.

The way you described the existing installation it's clearly at the load end. So I don't get how you can say this.

The more I think about it, I think 705 should say to apply the tap rules to any conductor that can be fed by two or more sources without an overcurrent device in between. But it doesn't.

 

[tortuga]

That would depend on what "supply" means.

Feeder #2, it just goes from the feed thru lugs to the 'line side' of the breaker in loadcenter "B", I am considering all that the supply side.
More than 200A could never flow on feeder #2 for very long.
If another disconnect was tapped off feeder#2 for say a pump then that would be different.

 

[petersonra]

And courts consider the intention of the law all the time.

usually only when there is ambiguity.